1. Field of the Invention
The invention relates to an electric power steering apparatus.
2. Description of Related Art
Among electric power steering apparatuses (EPSs), there is an apparatus that is equipped with an automatic control function of controlling the travel path of a vehicle by changing the steering angle of the vehicle's steering road wheels independently of the steering operation performed by a driver. Examples of this manner of automatic control includes a so-called lane keep assist control of recognizing a travel lane and assisting in the travel of the vehicle along the travel lane (see, e.g., Japanese Patent Application Publication No. 2005-343260 (JP-A-2005-343260)), a so-called parking assist control of assisting in the parking into a parking space (see, e.g., Japanese Patent Application Publication No. 2004-345468 (JP-A-2004-345468)), etc. In many cases, these automatic controls are performed on the basis of an assist command that is input from a superior or host control device (superior or host ECU) via an in-vehicle network.
However, in the construction in which the assist command is transferred via a network, it is inevitable that, due to differences in the communication protocol or specifications, the transfer of the assist command is delayed and therefore the responsiveness declines. Therefore, in an environment with an external disturbance such as a slope of the road surface, side wind, etc., there is a tendency toward large fluctuations of the value of the assist command that is computed so as to control the steering angle position of the steering road wheels. In consequence, particularly in the automatic control that is executed at the time of high-speed travel of the vehicle, there is a possibility of the locus of travel of the vehicle being disturbed.